1. Technical Field
The present invention relates to an etching method and etching apparatus for etching a film to form a concave portion therein with the use of a photoresist mask.
2. Description of the Related Art
Recently a degree of integration in a semiconductor has been becoming increasingly higher. In association with technical improvements in resist materials and exposure technique to satisfy the need for more minute patterns formed on a wafer, an opening dimension has become substantially smaller. On the other hand, as the patterns formed on a wafer become smaller, requirements for precision in finished dimension of an opening of a hole (a contact hole or a via hole) or a width of a trench (a wiring groove) have become more and more strict.
To satisfy the needs, as described, for instance, JP 2003-282536A, proposes an idea in which a relation between the type or the feed rate of a reaction gas and an etching speed are determined in advance and the feed rate is controlled based on, for example, an etching depth.
In the photolithography, a finished state of a developed pattern is determined based on a lot of conditions including conditions for applying a resist, conditions for heating the applied resist, conditions for exposure, conditions for heating the exposed resist, and conditions for development treatment. Thus, it is practically impossible to obtain a uniform opening dimension of a photoresist mask, and the dispersion in opening dimension is unavoidable. Therefore, the finished dimension of the pattern after a film is etched may vary caused by the variation of the opening dimension.
If the finished dimension of a concave portion of a film that has been etched is deviated from the design value, a designed device performance cannot be obtained. Also, if the finished dimension is larger than the design value, adjacent via holes or adjacent contact holes are closer to each other, which may cause a short circuit between the holes. In addition, recently, a multilayered resist structure has been developed. However, when holes in an organic film in the bottom layer of the multilayered photoresist are close to each other, the photoresist may fall.
For the reasons as described above, even if process conditions for etching are determined based on a desired finished state after etching, the desired finished state may be influenced by the dispersion in the mask pattern formed in the previous process of the etching process, which is another reason for difficulty in miniaturization of patterns.